1. Field of the Invention
The present invention relates to a tray for housing semiconductor devices such ICs, and more particularly to a tray suited for housing and transporting thin semiconductor devices having leads on every lateral side.
2. Description of the Prior Art
As semiconductors such as ICs have been integrated more and more, they have become miniaturized more and more and thinner and thinner. Thus, it has become necessary to apply as small external shocks as possible to the devices, and the structure of the trays greatly influences the yield of the semiconductor devices.
Many semiconductor devices have wiring leads consisting of extremely thin metal wires extending externally from the semiconductor devices, and such a problem arises that leads are likely to be deformed or bent when the leads contact the corresponding inner walls of the pockets or the like in a tray.
As shown in FIG. 6, the conventional tray for semiconductor devices has rectangular pockets 24 defined by longitudinal and crosswise partition portions formed in the space defined by an outer peripheral frame 22 and a base 25 projectingly formed in each pocket 24. After semiconductor devices 26 have been loaded on the corresponding bases 25, another tray is mounted on the first tray. Thus, the semiconductor devices are housed in the combination of the trays.
Downward extending ribs surrounding the side walls of the upper portion of the semiconductor devices housed in the pockets 24 in the lower tray are formed on the undersurface of the upper tray 21, and an edge frame 28 extends along the whole periphery of the tray and projects downward from the undersurface of the tray.
In order to pile up trays, the edge frame 28 of the upper tray is fitted on the outer wall of the outer peripheral frame 22. A small space is provided between the inner wall of the edge frame 28 and the outer wall of the outer peripheral frame 22. The space is provided so as to admit dimensional tolerance between the upper and lower trays and is defined by a horizontal space d.sub.1.
In the conventional trays, the horizontal space d.sub.2 between the outer wall of the downward extending rib 27 and the inner wall of the corresponding pocket 24 is larger than the horizontal space d.sub.1 so that the downward extending ribs 27 do not contact the inner walls of the pockets even if the upper and lower trays are displaced horizontally from each other. The horizontal space d.sub.3 between the inner wall of the downward extending rib 27 and the lateral surface of the device 26 is slightly larger than the space d.sub.1 in such a manner that the downward extending rib 27 presses the corresponding device 26 even if displacement occurs between the upper and lower trays by a distance equal to the space d.sub.1.
When, however, the trays receive a large shock due to dropping of the tray during transportation, the trays are flexed and thereby locally applied with pressure. The upper side portions of some devices 26 are strongly pressed by the inner walls of the downward ribs 27, resulting in deformation of the devices. The upward extending ribs 29 projecting from the peripheral edges of the upper surfaces of the bases and holding the side walls of the lower portions of the devices are pressed against the side walls of the lower portions of the devices and broken. Further, the fractures of the broken ribs 29 deform and/or damage to the leads 26a of the devices occurs.